Wireless stereo sound speaker system and modulator-oscillator circuit

ABSTRACT

Portable wireless stereo sound transmitter and system including one transmitter adapted for connection to one sound source for transmitting sound by wave energy at one high frequency channel to first remote receiving station and another transmitter adapted for connection to another sound source for simultaneously transmitting sound from another sound source by wave energy at another high frequency to second remote receiving station. The novel FM modulator-oscillator includes the series connection of a transformer, an L-C tank circuit, and a capacitor with the collector and emitter electrodes of a transistor connected thereto.

United States Patent [72] Inventor Frank M. Kenney 2584 E. Maplewood Ave., Littleton, Colo. 80120 21 App]. No. 692,140

[22] Filed Dec. 20, 1967 JIIM 29, 1971 [45] Patented [54] WIRELESS STEREO SOUND SPEAKER SYSTEM AND MODULATORDSCILLATOR CIRCUIT 8 Claims, 3 Drawing Figs.

[52] U.S.CL 325/36, I 179/15,179/10011,325/105,332/ 16 [51] lnt.Cl 110451/04, 1104b 1/20, H03c 3/00 [50] Field otSearch... 325/36, 105; 179/13,]5, 100.11, 100.1, 100.2; 332/161 [56] References Cited UNITED STATES PATENTS 1,513,973 11/1924 Doolittle 325/36 2,712,596 7/1955 Sherman 325/36 2,771,584 11/1956 Thomas 325/105 3,105,938 10/1963 Onnigian et al... 325/105 3,108,234 10/1963 Burns 325/105 3,360,609 12/1967 Fenner 179/13 3,464,031 8/1969 Rosen 325/105 FOREIGN PATENTS 258,865 12/1927 Great Britain 325/36 Primary Examiner- Richard Murray Assistant Examiner-George G. Stellar Attorney-Ancel W. Lewis, Jr.

ABSTRACT:,Portable' wireless stereo sound transmitter and system including one transmitter adapted for connection to one' sound source for transmittingsound by wave energy at one high frequency channel to first remote receiving station and another transmitter adapted for connection to another sound source for simultaneously transmitting sound from another sound source by wave energy at another high frequency to second remote receiving station. The novel FM modulator-oscillator includes the series connection of a transformer, an L-C tank circuit, and a capacitor with the collector and emitter electrodes of a transistor connected thereto.

PATENTEU JUN29 l9?! sum 1 or 2 FIG. 2

lNVI-IN'IUR. Frank M. Kenney A TTOR/VE Y5 WIRELESS STEREO SOUND SFEAKER SYSTEM AND MQDULATOKLOSCILLATOR CIRCUHT This invention relates to stereo sound devices and more particularly to a portable stereo sound transmitter and wireless stereo sound system.

lt is common in homes and in offices to have stereo sound equipment such as tapes and record players and more recently stereo tapes are available as automobile accessories. Such equipment has the advantage of providing selectivity as to the type of music available to the listener. The present practice with such stereo equipment is to locate multiple speakers at various positions in the same room as the sound source or to locate the speakers in other rooms or at locations distant from the sound source and then to physically interconnect the sound source to the speakers with electric wiring or the like.

Such wired stereo installations have the disadvantages of wiring installation expense, the unsightly appearance of wires if installed after the building has been erected and also the wiring limits the range of sound transmission.

Accordingly, it is an object of this invention to provide a simple, durable and compact device for transmitting stereo sound.

Another object of this invention is to provide a solid state wireless transmitting device for stereo sound.

A further object of this invention is to provide a portable electric stereo sound device suitable for use on available electric power and in conjunction with available radio receiving equipment for home, office and recreation use.

It is still another object of this invention to provide a high fidelity stereo sound device and system.

A still further object of this invention is to provide a novel FM modulator-oscillator circuit.

Other objects, advantages and capabilities of the present invention will be more apparent as the following description proceeds, taken in conjunction with the' accompanying drawings in which:

FIG. 1 is a perspective view of a stereo sound equipment depicting features of the present invention;

FIG. 2 is a perspective view of the stereo transmitter device shown in FIG. 1 and drawn to an enlarged scale with portions of the outer casing or body broken away to show interior parts; and

FIG. 3 is one form of an electric circuit diagram of the transmitter device shown in FIG. 2.

Referring now to the drawing and particularly MG. 1, there is shown a typical relative arrangement of electrical equipment which in general includes a sound source 11, a transmitter device 12 and a pair of spaced remote receiving stations 13 and 14. The sound source 11 may be of various types of commonly available stereo equipment, such as a stereo tape recorder as depicted, a stereo record player or the like which produces separate electrical signals representing sound, typically music, reproduced from two different sources.

The transmitter device 12 is interconnected with the sound source by separate electric lines 15 and 16 and transmits such sounds on separate channels to the distant receiver stations 13 and 14 with one receiver station being tuned to the transmitting frequency of one channel and the other receiving station being tuned to the transmitting frequency of the second channel. The antennas of the transmitter device and the receiving stations are depicted schematically in FIG. 1 for purposes of illustrating two channels of transmission from transmitter device 12. It is, therefore, apparent that there is no physical connection between the transmitter device 12 and the receiving stations 13 and 14 other than by radio wave links.

The receiving stations may be, for example, various types of radio sets having inter alia, an antenna, an L-C tank circuit, a detector and speakers to reproduce the sound at any location where such receiving stations are positioned. These receiving stations may be located in a wide variety of places, as for example, in a typical home installation; the recorder or sound source 11 will be in one room and the receiving stations 13 and M in another room or in a yard location such as on the patio. Another example for recreational purposes would be to have a stereo tape recorder 11 and transmitter device 12 in the automobile with the receiving stations remote from the automobile, such as on a picnic table.

The transmitter device 12 may preferably be constructed in the form of a single boxlike body or unit 2% which is small in size and durable in construction which may be located either on or in adjoining relation to the sound source 11 and will operate on standard voltages, such as l 15 volt AC. The external structure on this boxlike body supports a first channel jack or input terminal 21, a second channel jack or input terminal 22, an on/off light 23 and an on/off switch 243 and an electric cord and connector 25 extending from one wall of the box to be inserted into a power outlet (not shown).

lnteriorly of the body, l prefer to have separate modules for each channel generally depicted in the form of separate detachable flat panel boards 26 and 29 or the like on which are carried the electrical components as described hereafter. The electric circuitry for each channel of transmission herein referred to as the left and right side channels with L and R used for designation purposes will include an L-C tank circuit having an RF variable inductor or coil designated 271. on board 26 and 27R on board 29.

One preferred form of variable inductor has an adjustable core or slug 27a which threads into the core and has a 0.17 to 0.27 microhenry range. An inductor which has been found to be particularly suitable in this circuitry is the .l. W. Miller No. 4301. This inductor provides both the required characteristics for oscillation and in addition radiates RF energy to act as the antenna for the transmitter circuit.

Variable or adjustable capacitors designated 28L on board 26 and 28R on board 29 are connected in parallel with adjoining inductors 271. and 27R, respectively, and each has an adjustable screw 28a for varying the capacitance. The range of these capacitors are, 2 to 25 pf. While specific components have been described, it is understood that various types of equivalent electric components may be used on boards 26 and 29 including printed circuitry.

Referring now to the circuit diagram of FIG. 3, one preferred arrangement of electric circuitry for transmitter device 12 has separate transmitter portions for the separate channels of transmission and each is enclosed in dash lines and designated 31L and 31R for convenience of description'with one transmitter portion 31L having input terminal 21 and the other transmitter portion 31R having input terminal 22 above referred to. Separate power portions are provided which are enclosed in dash lines and designated 33L and 33R and are electrically associated with transmitter portions 31L and 31R, respectively.

Each said transmitter portion 31L and 31R and power portion 33L and 33R is of similar circuitry so that a description of one applies to both and like numerals are applied to both with the L and R referring to the left and right side channels of transmission to distinguish one from the other. Each of the power portion circuits 33L and 33R is preferably of the solidstate type and is connected between the electric power cord and connector 25 and an associated transmitter portion. Each power portion circuit includes a stepdown transformer 41 having its primary winding connected across the cord and connector 25. A full-wave rectifier arrangement is connected across the secondary winding of transformer 41 which includes solidstate diodes 42 and 43, each having one electrode connected to one side of the secondary and the other electrodes connected together. A load resistor 44 and filter capacitor 45 is connected across a center tap on the secondary winding and the common connection of the diode electrodes.

A power amplifier transistor 46 has its emitter connected to the load resistor and its base connected to an adjustable tap on load resistor 44 through a bias resistor 47. This transistor has a filter capacitor 48 and resistor 49 connected across its collector so as to provide a low DC voltage at the output at a terminal designated 50. A suitable voltage is 9 volts DC. While separate power source portions 33L and 33R have been shown and described, it is understood that a single power circuit may be utilized to provideDC electric power to each transmitter portion circuit.

ln one of the input lines between cord and connector 25 and the primary winding of the stepdown transformer, there is located the on/off switch 24 and an overload protector 51 is connected in the other input line. The on/off light 23, preferably a neon lamp, is connected across the input lines between cord and connector 25 and switch 24 and has a current limiting resistor 52.

Each of the transmitter portion circuits 31L and 31R is preferably suitable for frequency modulation of the sound signals, although it is understood that the spirit and scope of the present invention is not limited to frequency modulation butmay also be carried out with amplitude modulation. The term high frequency as used herein is preferably in the range of 87 to 108 megacycles.

Each of the'transmitter portion circuits 311.. and 31R has an oscillator circuit which includes the above referred to variable inductor or coil designated 27L and 27R, respectively, and variable capacitors designated 28L and 28R, respectively, which are interconnected in parallel as above described to form separate L-C tank circuits for the left and right side channels.

For each channel this oscillator circuit also includes an oscillator transistor 61 interconnected between the power source terminal 50 and one side of the L-C tank circuit. Bias resistors 62 and 63 are connected across output 50 with the base element of transistor 61 between these resistors. bypass capacitor 64 is connected between power terminal 50 and the base electrode of transistor 61. The collector electrode is connected to one side of the tank circuit. A coupling capacitor 66 is connected between the emitter and collector electrodes. One transistor 61 found to be suitable in this circuit is the Motorola HEP-1 RF mixer oscillator transistor.

At the sound or audio input side of each transmitter portion between the input terminal and the other side of the tank circuit proceeding from the input terminal to the. tank circuit, there is provided a high impedance resistor 71, a coupling capacitor 72, an audio amplifier transistor 73 and a stepdown transformer 74. The input impedance 71 is a matching impedance for the output of the recorder 11 or like sound source and for such equipment-which may be on the order of 1.5 to 2.5 megohms. One transistor 73 found to be suitable in this circuit is the GE 2 audio amplifier transistor. Bias resistors 75 and 76 are connected to the base electrode of the transistor and the R-C series circuit of resistor 71 and coupling capacitor 72 is connected to the base electrode of the transistor 73. A bias resistor 77 and bypass capacitor 78 connected in parallel and they are connected between the emitter electrode and power source terminal 50. The primary winding of transformer 74 is connected to the collector electrode and the secondary circuit is connected to the L-C tank circuit. A coupling capacitor 79 is connected between the tank circuit and power source terminal 50.

The resonating frequency of each tank circuit is set and adjusted by adjusting its variable capacitor and variable inductor. In one preferred practice, the left side transmitter portion 31L for the left side channel will transmit at about 91 megacycles and the right side transmitter-portion 31R for the right side channel will transmit at about 94 megacycles.

Referring now to FIG. 3 of the drawings, the modulatoroscillator circuit will now be generally explained with reference to the right channel. The electric stereo signals which have been amplified by transistor 73 appear at the secondary of the winding of transformer 74 and are applied to a modulator-oscillator network including the parallel tank circuit consisting of inductor 27R and capacitor 28R which in turn are connected in series with a feedback capacitor 66. One plate of the feedback capacitor 66 is connected to the emitter and the other plate to the collector of an oscillator transistor 61 which is connected in a common-base configuration. The emitter of transistor 61 is biased by a connection to one side of the secondary of transformer 74 through capacitor 79 and resistor 65 and the collector of transistor 61 is biased by a connection to one side of the secondary of the transformer 74 through the tank circuit. The base being common to the collector and emitter is biased by the voltage divider comprised of resistors 62 and 63. The other side of the secondary of transformer 74 is connected to one side of the primary winding of transformer 74 which connects the modulating signals to the base of the transistor 61 through biasing resistor 63. in this way the potentials at the emitter and collector of transistor 61 vary in phase with the modulating signals and whereby the transistor 61 operates as an amplifier to counteract the losses and the feedback capacitor 66 serves to change the effective capacitance of the resonant tank in a direct relation so that the oscillations in the tank vary at a rate proportional to the frequency of the modulating signals. The result is frequency modulation of the carrier signal and audible stereo signals are transmitted via wave energy from the inductor 27.

While it is preferred to eliminate a separate antenna coil inductively coupled to the tank coil as above described it has been found that a separate folded dipole-type antenna is also suitable in the above described circuit.

While the present invention has been described with reference to particular structure and preferred electric components, there is no intent to limit the spirit and scope of the present invention to this structure and components except as defined by the appended claims.

1 claim:

1. A wireless stereo sound speaker system comprising: a first FM transmitter including first input terminals for supplying recorded electric stereo signals from a first sound track, a first coupling transformer receiving the first track stereo signal and having a primary and secondary winding with a common terminal, first modulator-oscillator circuit coupled to said first coupling transformer for frequency modulating a radio frequency carrier signal produced in a tank with said first track stereo signal and radiating the resulting modulated carrier signal as wave energy along a first channel; and a second F M transmitter including second input terminals for supplying the recorded electric stereo signal from a second sound track, a second coupling transformer receiving the second track stereo signal and having a primary and a secondary winding with a common terminal, and a second modulator-oscillator circuit coupled to said second coupling transformer for frequency modulating a second radio frequency carrier signal at a different frequency from said first carrier signal with said second track stereo signal and radiating the resulting second modulated carrier signal as wave energy along a second channel simultaneously with said first transmitter, each said modulator-oscillator circuit including a parallel connected inductor-capacitor tank and a feedback capacitor having a pair of plates connected in series with the tank, said tank being connected to one side of said secondary winding and a transistor oscillator connected in a common-base configuration, said transistor having emitter, base and collector electrodes, one of said plates being connected to said collector and the other of said plates to said emitter, said base being coupled to said common terminal to apply the modulating signals to said base; and first and second receiver at a location remote from said first and second transmitters, said first receiver being tuned to said first carrier signal frequency for reproducing stereophonic sounds from the electric stereo signals transmitted from said first transmitter and said second receiver at a selected spaced distance from the first receiver being tuned to the carrier frequency of said second transmitter for reproducing audible stereophonic sounds from the electric stereo signals transmitted from said second transmitter, each said first and second receivers having an intensity control to provide a phase balance in the sound being reproduced by said receivers at a listeners ears.

2. A wireless stereo sound speaker system as set forth in claim 1 including a DC power supply for each said modulatoroscillator circuit having a solid-state diode bridge rectifier, a pi section filter coupled to the output of the bridge rectifier and at least one power transistor coupled to the output of the pi section filter.

3. A modulator-oscillator circuit for frequency modulating a carrier signal comprising a coupling transformer having a primary and a secondary winding for supplying modulating signals from a signal source, said secondary winding having a first terminal in common with a primary terminal and having a second terminal, a parallel connected inductor-capacitor tank circuit, a feedback capacitor having a pair of plates, said feedback capacitor being connected in series with the tank, an oscillator transistor including an emitter, collector, and base, said transistor being connected in a common-base configuration, one of said plates being connected to said collector and the other of said plates being connected to said emitter, said collector being coupled to said second terminal through said tank circuit to bias saidcollector with the modulating signals, said emitter being coupled to said second terminal to bias said emitter with the modulating signals and said base being coupled to the common terminal to apply the modulating signals to said base whereby the potential at said emitter and collector vary in phase with the modulating signals applied to said terminals, said transistor operates as an amplifier to counteract losses and said feedback capacitor serves to change the effective capacitance of said tank circuit in a direct relation so that the oscillations in said tank circuit vary at a rate proportional to the amplitude of the modulating signals and produce a frequency modulated carrier signal as wave energy from said tank circuit.

4. A modulator-oscillator circuit as set forth in claim 3 wherein said emitter is coupled to said second terminal through a resistor and a capacitor.

5. A modulator-oscillator circuit as set forth in claim 3 wherein said base is biased by a voltage divider to establish a reference for the modulating signals being applied to the emitter and collector.

6. A modulator-oscillator circuit as set forth in claim 3 wherein the capacitor and inductor in said tank circuit are variable to change the frequency of the oscillations of the tank circuit.

7. A modulator-oscillator circuit as set forth in claim 3 wherein the inductor forms the antenna for transmitting the modulated carrier signal as wave energy.

8. A modulator-oscillator circuit as set forth in claim 3 including means for amplifying the modulating signals before applying them to said coupling transformer. 

1. A wireless stereo sound speaker system comprising: a first FM transmitter including first input terminals for supplying recorded electric stereo signals from a first sound track, a first coupling transformer receiving the first track stereo signal and having a primary and secondary winding with a common terminal, first modulator-oscillator circuit coupled to said first coupling transformer for frequency modulating a radio frequency carrier signal produced in a tank with said first track stereo signal and radiating the resulting modulated carrier signal as wave energy along a first channel; and a second FM transmitter including second input terminals for supplying the recorded electric stereo signal from a second sound track, a second coupling transformer receiving the second track stereo signal and having a primary and a secondary winding with a common terminal, and a second modulator-oscillator circuit coupled to said second coupling transformer for frequency modulating a second radio frequency carrier signal at a different frequency from said first carrier signal with said second track stereo signal and radiating the resulting second modulated carrier signal as wave energy along a second channel simultaneously with said first transmitter, each said modulator-oscillator circuit including a parallel connected inductor-capacitor tank and a feedback capacitor having a pair of plates connected in series with the tank, said tank being connected to one side of said secondary winding and a transistor oscillator connected in a common-base configuration, said transistor having emitter, base and collector electrodes, one of said plates being connected to said collector and the other of said plates to said emitter, said base being coupled to said common terminal to apply the modulating signals to said base; and first and second receiver at a location remote from said first and second transmitters, said first receiver being tuned to said first carrier signal frequency for reproducing stereophonic sounds from the electric stereo signals transmitted from said first transmitter and said second receiver at a selected spaced distance from the first receiver being tuned to the carrier frequency of said second transmitter for reproducing audible stereophonic sounds from the electric stereo signals transmitted from said second transmitter, each said first and second receivers having an intensity control to provide a phase balance in the sound being reproduced by said receivers at a listener''s ears.
 2. A wireless stereo sound speaker system as set forth in claim 1 including a DC power supply for each said modulator-oscillator circuit having a solid-state diode bridge rectifier, a pi section filter coupled to the output of the bridge rectifier and at least one power transistor coupled to the output of the pi section filter.
 3. A modulator-oscillator circuit for frequency modulating a carrier signal comprising a coupling transformer having a primary and a secondary winding for supplying modulating signals from a signal source, said secondary winding having a first terminal in common with a primary terminal and having a second terminal, a parallel connected inductor-capacitor tank circuit, a feedback capacitor having a pair of plates, said feedback capacitor being connected in series with the tank, an oscillator transistor including an emitter, collector, and base, said transistor being connected in a common-base configuration, one of said plates being connected to said collector and the other of said plates being connected to said emitter, said collector being coupled to said second terminal through said tank circuit to bias said collector with the modulating signals, said emitter being coupled to said second terminal to bias said emitter with the modulating signals and said base being coupled to the common terminal to apply the modulating signals to said base whereby the potential at said emitter and collector vary in phase with the modulating signals applied to said terminals, said transistor operates as an amplifier to counteract losses and said feedback capacitor serves to change the effective capacitance of said tank circuit in a direct relation so that the oscillations in said tank circuit vary at a rate prOportional to the amplitude of the modulating signals and produce a frequency modulated carrier signal as wave energy from said tank circuit.
 4. A modulator-oscillator circuit as set forth in claim 3 wherein said emitter is coupled to said second terminal through a resistor and a capacitor.
 5. A modulator-oscillator circuit as set forth in claim 3 wherein said base is biased by a voltage divider to establish a reference for the modulating signals being applied to the emitter and collector.
 6. A modulator-oscillator circuit as set forth in claim 3 wherein the capacitor and inductor in said tank circuit are variable to change the frequency of the oscillations of the tank circuit.
 7. A modulator-oscillator circuit as set forth in claim 3 wherein the inductor forms the antenna for transmitting the modulated carrier signal as wave energy.
 8. A modulator-oscillator circuit as set forth in claim 3 including means for amplifying the modulating signals before applying them to said coupling transformer. 